1. Field
One embodiment of the invention relates to a test device for a magnetic storage device comprising a magnetic disk, a magnetic storage device including the test function, and a method of manufacturing the magnetic storage device.
2. Description of the Related Art
Hard disk drives (HDD) are widely used as storage devices for computers. In order to increase the recording density of a magnetic disk in a HDD, it is important to reduce the flying height of a head element floating from a magnetic disk surface. Recently, to further reduce the flying height of the head element, a technology called dynamic flying height (DFH) has been noted. The DFH technology is characterized in that a magnetic head has a function of correcting the flying height. Specifically, a heater is incorporated near a magnetic gap of the magnetic head. When an electric power is supplied to the heater, the heater generates heat, leading to heat expansion near the magnetic gap. The heat expansion causes protrusion of the magnetic gap toward the magnetic disk surface side, and consequently the flying height is reduced.
There is a HDD that has such a DFH function and monitors a resistance value of a heater to detect degradation over time of the heater's resistance (for example, see Japanese Patent Application Publication (KOKAI) No. 2007-294007). Before shipment of the HDD, an adjustment process is performed through the DFH function to optimize the flying height of the head element. In the adjustment process, the electric power supplied to the heater is increased to bring the head element into contact with the magnetic disk surface. This operation is called “touchdown” of the head element. The electric power supplied to the heater is reduced from this state to gradually float the head element, and the electric power supplied to the heater upon reaching a desired flying height is detected and utilized as a controlled variable of the heater during normal operation.
In the magnetic head having the DFH function, the supply of excessive electric power to the heater causes plastic deformation around the head element such that the head element may not return to its original position even if the supplied electric power is reduced. For example, to perform “touchdown” of the head element in the adjustment process, a relatively high electric power is supplied to the heater. To increase the variable range of the flying height by the DFH, the maximum electric power supplied to the heater needs to be increased. However, when excessive electric power is supplied to the heater and plastic deformation is caused around the head element, it becomes impossible to float the head element normally and to use the magnetic head. To prevent this, it is preferable to be able to detect the plastic deformation around the head element, but no means have been considered to enable the detection of the plastic deformation without increasing the cost for manufacturing and components of the HDD.